1. Field of the Invention
The present invention relates generally to the field of wireless communication, and particularly to the design of an antenna.
2. Description of Related Art
Small antennas are required for portable wireless communications. To produce a resonant antenna structure at a certain radio frequency, it is usually necessary for the structure to be of a size equal to one-half of the electromagnetic wavelength, or for some designs, one-quarter of the electromagnetic wavelength. This is usually still too large.
A conventional solution, to reduce the size further., is to reduce the effective wavelength of the electromagnetic waves, by inserting a material of a high dielectric constant. Then, the internal wavelength is reduced by the square root of the dielectric constant. This requires special high dielectric constant materials that add cost, weight and cause an efficiency penalty. Accordingly, the present invention addresses these needs.
The present invention provides an effective increase in the dielectric constant purely by geometry, using a spiral sheet configuration. The dielectric material can have a dielectric constant  greater than 1, or it can simply be air with dielectric constant 1. Therefore cheaper dielectric materials can be used. Indeed there is nothing cheaper than air.
An antenna, comprising a first plate and a second plate, the combination of the first and second plates serving as a capacitive structure; and a third metallic structure, coupled to the first and second plates, thereby producing a cylindrical or substantially cylindrical current distribution, with two openings or holes at either end of the cylinder-like shape. Although a cylindrical current distribution is described, other shapes of current distribution can be practiced provided that the current is distributed around two openings or holes, that would construct an antenna without departing from the spirit of the present invention. In effect, the overlap between the first and second plates, on the edge of the cylinder, forms a seam between the two holes at the ends of the cylinder-like structure.
Advantageously, the present invention discloses an antenna structure that is more compact, reducing the overall size of a wireless device. The present invention further advantageously reduces the cost of building an antenna by using air as the dielectric. .
Other structures and methods are disclosed in the detailed description below. This summary does not purport to define the invention. The invention is defined by the claims.